1. Field of the Invention
The present invention relates to helix-coupled vane lines or structures and to the electron tubes comprising such lines, notably wideband crossed-field amplifiers.
It relates more particularly to a method for making helix-coupled vane lines such as these.
Wideband amplification is obtained, broadly speaking, by the interaction of a space charge wave conveyed by an electron beam and a microwave borne by a slow-wave line. During the interaction, there is synchronism between the electrons of the beam and the microwave.
2. Description of the Prior Art
Of the difficulties that arise in the development of crossed-field amplifiers, a large part is related to the designing of slow-wave lines.
To obtain a wide operating band, it is sought to make the dispersion of the line as small as possible and the coupling impedance as great as possible. These two conditions are contradictory and compromises have to be accepted.
Helix-coupled vane lines, also called helix-on-base lines have been developed with good results. They work in the fundamental mode. The helix, which has a length of several octaves, has each of its turns fixedly joined to a quarter-wave vane (or base). The vanes are all fixed to one and the same support which may be the casing, under vacuum, of the tube. These helix-coupled vane lines are far lighter and far more compact than other lines formed by waveguide elements, and they generate fewer parasitic oscillations.
The helix-coupled vane lines are generally curved in the form of a ring, but the two ends of the helix are not joined. There also exist lines such as these that are rectilinear. There also exists a known way of using lines with two helical lines fixedly joined to the same vanes. It is thus possible to obtain higher power values, essentially higher mean power values.
To make this helix-coupled vane line, each turn of a helix is brazed to vanes that are fixedly joined to one and the same support. This is a very delicate operation to perform, especially if the line is designed to be mounted in a tube working at high frequencies for the diameter of the wires forming the helix is extremely small: for example, it is of the order of one-tenth of a millimeter. It is difficult to make satisfactory contacts between one turn and another, and ensure the mechanical regularity of the position of each turn.
The matching of the crossed-field tubes using lines obtained by this method is difficult to reproduce from one tube to another. This method requires tools that are carefully designed and, therefore, expensive. The cost of manufacture of such tubes is then especially high.